First cookbook example for the docs: Hello World in C.

Documentation/cookbook/hello/hello.do

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+# If hello.c changes, this script needs to be
+# re-run.
+redo-ifchange hello.c
+
+# Compile hello.c into the 'hello' binary.
+#
+# $3 is the redo variable that represents the
+# output filename.  We want to build a file
+# called "hello", but if we write that directly,
+# then an interruption could result in a
+# partially-written file.  Instead, write it to
+# $3, and redo will move our output into its
+# final location, only if this script completes
+# successfully.
+#
+cc -o $3 hello.c -Wall